外源细胞分裂素对玉米叶原基分化类型的调控

以互生玉米自交系H4d、8701d为材料，取自交授粉12 d的幼胚，分别在含不同浓度6-BA的脱分化培养基上诱导愈伤组织，筛选II型愈伤组织，分别转入0~3 mg L1 6-BA浓度梯度的分化培养基上诱导出芽。芽点出现时，在解剖镜下剥离顶端分生组织，电镜扫描观察叶原基形态，并用ELISA反应测定顶端分生组织细胞分裂素6-BA、ZRs、DHZRs、iPAS和生长素IAA、NAA含量。结果表明，外源细胞分裂素6-BA可调控互生基因型玉米材料幼苗叶原基转换为对生甚至畸形叶原基类型，6-BA浓度越高、处理越早，出现对生叶原基、畸形叶原基的频率越高。ELISA反应显示，生长点激素含量的改变是外源激素的吸收累积造成的，内源细胞分裂素的含量并未明显改变，在互生基因型下通过增加外源细胞分裂素6-BA提高细胞分裂素/生长素值可导致叶原基分化类型向对生、畸形类型转换，解除外源激素作用后，生长点细胞分裂素/生长素值的恢复导致叶原基分化类型返回原始基因型类型。这进一步证实生长点细胞分裂素/生长素是决定玉米叶原基分化类型的关键因素。

Differentiation of Leaf Primordium in Maize Regulated by Exogenous Cytokinin

The 12-day immature embryos of 2 maize (Zea mays L.) inbred lines with alternative phyllotaxy, 8701d and H4d, were cultured on media with different contents of 6-BA for 14 d to produce calluses, which were further subcultured twice on the same media. Type II calli were established on the differentiation mediums with 0–3 mg L^-1 of 6-BA content ladder to induce sprout formation. Sprouts in shoot tips were peeled off under a dissecting microscope and the images of the phyllotactic patterns of leaf primordium were taken by scanning electron microscope. The contents of 6-benzylaminopurine (6-BA), zeatin riboside group (ZRs), dehydro zeatin riboside group (DHZRs), isopentenyladenosine group (iPAs), napthalene acetic acid (NAA), and indole-3-acetic acid (IAA) in shoot apical meristem were measured by ELISA method. Three phyllotactic patterns, namely opposite, misshapen, and alternate were observed in the leaf primordium. In H4d plants, exogenous application of the cytokinin 6-BA induced a change in the phyllotaxy of shoot apical meristem (SAM) from alternate to opposite and misshapen. Higher 6-BA content and earlier treatment led to higher proportions of SAM with misshapen leaf primordia and opposite leaf primordia. The cytokinin/auxin (CTK/AUX) ratio in SAM with misshapen leaf primordia was higher than that with decussate leaf primordia, which in turn, was higher than that with alternate leaf primordia. The accumulation of cytokinin 6-BA increased the levels of cytokinin in SAM, but did not change the levels of endogenous cytokinins (ZRs, DHZRs, and iPAs). The comeback of CTK/AUX ratio in tissue cultured immature seedlings could induce the leaf primordium of them to come back to the original phyllotactic patterns. The CTK/AUX ratio is the determinative factor that regulates the differentiation of maize leaf primordium.